The present invention relates to inspection of patterns and/or foreign matters, for detecting or examining defects, such as short-circuit and/or open-circuit or the like, on the patterns as a target of inspection, and relates, in particular, to a method and an apparatus, for inspecting the defects and/or foreign matters of the patterns formed on, such as, a semiconductor wafer, a liquid crystal display, and a photo-mask, etc., for example. Hereinafter, it is assumed that the defects include the foreign matters, in the meaning thereof.
Conventionally, in such kind of an inspection apparatus, as is described in Japanese Patent Laying-Open No. Hei 7-318326 (1995) <hereinafter, conventional art 1>, an image is detected on the patterns to be examined or inspected by means of an image pick-up element, such as a line sensor, etc., while moving the patterns to be inspected, so as to compare an image signal detected with one which is delayed by a predetermined time in gradation thereof, thereby acknowledging inconsistency or anti-coincident to be a defect.
Also, other conventional art, relating to the defect inspection of patterns to be inspected, is known from Japanese Patent Laying-Open No. Hei 8-320294 (1996) <hereinafter, conventional art 2>. In this conventional art 2 is described a technology, for examining the patterns to be inspected, for example, a semiconductor wafer, in which areas high pattern density, such as the memory mat portions, etc., and low pattern density, such as peripheral circuit portions, etc., are mixed with each other, wherein gradation conversion is conducted on digital image or video signal, which is obtained through A/D conversion of the image signal detected, so that a predetermined relationship can be established between the high density areas and the low density areas on the patterns to be inspected, in particular in the brightness or the contrast thereof, rather than the frequency distribution thereof, and this image signal converted in gradation is compared with other gradation conversion image signal for comparison, under the condition of being fitted to each other in position, thereby inspecting minute or microscopic defects thereon with high accuracy.
Furthermore, the conventional art for inspecting the patterns on a photomask is already known, for example, Japanese Patent Laying-Open No. Hei 10-78668 (1998) <hereinafter, conventional art 3>. In this conventional art, it is described that the UV light rays are irradiated upon the mask, equally, in which coherence is lowered by rotating a diffuser panel inserted within an optical path, with using a UV laser beam as a light source, such as, an excimer laser or the like, so as to calculate out a characteristic amount or quantity from the obtained image data of the mask, thereby deciding or examining good or bad, i.e., the quality thereof. And, a projection exposure apparatus with using an excimer laser therein is already known, for example, in Japanese Patent Laying-Open No. Sho 59-226317 (1964) or Japanese Patent Laying-Open No. Sho 62-231924 (1987), etc.
For LSI manufacturing in recent years, the circuit patterns formed on a wafer come to be minimized, such as, 0.25 μm or less than that in the pattern width thereof, responding to the needs of high integration; thus it nearly reaches up to the limit on the resolving power of an image-forming optical system. For this reason, development is advanced on application of high NA technology or an optical super resolving power technology.
However, the NA technology also reaches up to the limit thereof, physically. Accordingly, a substantial or intrinsic approach is trying to shift the light wavelengths to be applied for the detection into the regions of the UV light and DUV light, i.e., shortening the light wavelength.
Further, due to the necessity of conducting the inspection with high speed, it is impossible to adopt the method of scanning the laser beam focused or converged thinly on a sample. On the contrary, when trying to illuminate with irradiating the laser beam spreading out all over a visual field, however the illumination of the laser beam generates speckles, or an overshoot or an undershoot, being called by a “wringing”, at an edge portion of the circuit pattern, thereby bringing about a problem that the image cannot be obtained of good quality.